1. Field of the Invention
The present invention concerns a spectacle frame having a substantially vertical front when placed on the head of the user, and connected at either side by a hinge to a horizontal side arm for hooking the frame over the ears.
2. Definition of Related Art
A so-called "resilient" hinge allows the arm to move by rotation under tension in a substantially horizontal plane from one so-called "closed" position where this arm is practically parallel to the front, the frame being ready for insertion in a pocket or in a case, to a so-called "open" position where the arm is practically at right angles, the frame being ready to wear. This hinge may also provide a complementary resilient movement of the arm outwards beyond its open position. Such hinges then provide an element of comfort in the wearing of spectacles which is much appreciated by the public, in particular on account of the fact that the arms lie against the temples with a reasonable amount of pressure.
A hinge generally consists on the one hand of a front knuckle fixed to a front side lug, which lug may be straight, overlapping, rolled or elbowed; and on the other hand by an arm knuckle connected directly or indirectly to the end of the arm, a hinge pin providing a connection between the knuckles. The term female knuckle is used to designate a part comprising two eyeholes one above the other in the manner of a fork, and receiving in the middle the single eyehole of a male knuckle.
In a first type of resilient hinge, the periphery of the male knuckle has a cam shape, in particular having two notches defining the open and closed positions respectively, a cam against which a ball is pressed by a spring, both being installed in a housing provided opposite each other in the female knuckle. These complex hinges are described for example in documents FR 1 120 399 or EP 0 137 885.
In a second type of resilient hinge, capable of turning beyond the open position, the arm knuckle is connected to the arm in a telescopic manner by a complex resilient return mechanism, and the end of this arm rests against the lug situated in its alignment. Thus, when the arm moves beyond its open position, the inner edge of the end of the arm moves away from the fixed knuckle in a sort of rotation about the pivot point, a movement which compresses or extends the spring of the return mechanism. Conversely, when the arm returns towards its closed position, the cam-shaped periphery of the front knuckle pushes back the cap of the housing of the mechanism, which once more compresses or extends the spring. Such complicated hinges are for example described in the documents FR 1 511 263 or FR 2 609 816.
The document FR 2 057 408 describes another type of resilient hinge having a male front knuckle and a female arm knuckle connected by a hinge pin. The upper face of the male knuckle in contact with the upper eyehole of the female knuckle is flat, whereas the lower face is formed of a cruciform notch (or double hollow) interacting with a raised portion (or boss) with an oblique side on the lower eyehole of the female knuckle. This lower eyehole is flexible towards the bottom so as to move away when the arm is opened, the male knuckle remaining at a point in contact with the upper eyehole enclosed in the arm. The resilience of this hinge based on the flexing of all of a lower eyehole proves however too slack with time to be reliable.
The main disadvantage of these resilient hinges lies above all in the fact that the initial part of the lug and/or the arm outside its respective knuckle is of necessity bulky in order to house the resilient mechanism. The appearance of this is not particularly aesthetic, especially when the main part of the lug or the arm is reduced to a simple rod.